1. Field of Invention
The present invention relates to a lens module, and more particularly to a zoom lens module.
2. Description of Related Art
FIG. 1 is a schematic view of a conventional manual focus lens module. Referring to FIG. 1, in the conventional lens module 10, a lens 110 passes through an inner ring 120, and the inner ring 120 is disposed against and between a focus ring 130 and a spring 140. Due to the focus ring 130 having segmented steps, when manually turning the focus ring 130, the inner ring 120 and the lens 110 are driven to move up and down along a Y axis, so as to achieve focusing. However, the lens module 10, due to the manual focus, is inconvenient in use.
FIG. 2 is a schematic view of a conventional lens module using a step motor to focus. Referring to FIG. 2, in the conventional lens module 20, a lens 110 passes through an inner ring 120, and the inner ring 120 is disposed against and between a focus ring 130′ and a spring 140. The focusing manner of the lens module 20 involves controlling a step motor 150 to drive a transmission mechanism, e.g. a screw, a turbine, a gear, or the focus ring 130′ in an electromotive manner, so that the inner ring 120 and the lens 110 are driven to move up and down along a Y axis, thereby achieving focusing. The lens module 20 can achieve an automatic focus, but has a large volume and high manufacturing cost, and is high power consuming when focusing.
FIG. 3A and FIG. 3B are schematic views of two conventional lens modules both using a voice coil motor to focus. Referring to FIG. 3A first, in the conventional lens module 30, a lens 110 passes through a magnetic conductive inner ring 160, and an force-at-a-distance is generated between magnets 170 disposed on both sides of the magnetic conductive inner ring 160 and the magnetic conductive inner ring 160 to prevent the magnetic conductive inner ring 160 moving left and right, thus fixing the position of the lens 110 on an X axis. In addition, the focusing manner of the lens module 30 involves controlling the magnitude of the current provided into a coil 180, so as to produce different magnetic levitation forces to drive the magnetic conductive inner ring 160 and the lens 110 to move along a Y axis, thereby achieving focusing.
The lens module 30 has a slow focus speed. After completing focusing, a current must be continuously provided into the coil 180 to prevent the elastic force g of the spring 140 from urging the magnetic conductive inner ring 160 moving downward, such that the position of the lens 110 can be maintained. Thus, the conventional lens module 30 is high power consuming in use. And, the position of the lens 110 on an X axis is fixed by the force-at-a-distance, so that the lens 110 tends to be inclined. Moreover, the lens module 30 cannot stand vibration or falling test.
Referring to FIG. 3B, in the conventional lens module 40, a lens 110 passes through a magnetic conductive inner ring 160′, and a guide rod 185 is used to prevent the magnetic conductive inner ring 160′ moving left and right, so as to fix the position of the lens 110 on an X axis. In addition, a sensor 190 is used to detect the position of the magnetic conductive inner ring 160′ on a Y axis, and send a signal back to an application specific integrated circuit (ASIC) 195. The ASIC 195 drives a coil 180 in accordance with the position of the magnetic conductive inner ring 160′, so as to move the magnetic conductive inner ring 160′ and the lens 110 to the desired positions, thereby achieving focusing. It should be noted that after the lens module 40 completes focusing, no current is provided into the coil 180. However, the manufacturing cost thereof is high.
FIG. 4 is a schematic view of a conventional two-stage electromotive focus lens module. Referring to FIG. 4, in a lens module 50, a lens 110 passes through an inner ring 120′, and a ring magnet 196 is disposed outside the inner ring 120′. The focusing manner of the lens module 50 involves changing the direction of the current provided into a coil 180 to produce an attractive force or a repulsive force between the coil 180 and the ring magnet 196, so as to drive the ring magnet 196, the inner ring 120′, and the lens 110 to move along a Y axis to the top side or bottom side. In addition, as a magnetic conductive plate 197 is partially magnetized, after completing focusing and stopping providing the current into the coil 180, if the lens 110 moves to the top side, an attractive force is generated between the magnetic conductive plate 197 above and the ring magnet 196, so as to fix the lens 110 at the top side. Similarly, if the lens 110 moves to the bottom side, an attractive force is generated between the magnetic conductive plate 197 below and the ring magnet 196, so as to fix the lens 110 at the bottom side.
The lens module 50 can only switch focusing between two stages and has a large volume. Additionally, due to the high cost of the ring magnet 196, the manufacturing cost of the lens module 50 is increased accordingly.